Flow meter



M. DAVIS FLOW METER April 4, 1967 2 Sheets-Sheet 1 Filed Dec.

I NVEN TOR.

A rzmzy April 4, 1967 M. DAVIS 3,312,1Gfi

FLOW METER Filed Dec. '7, 1964 2 Sheets-Sheet 2 I NVENTOR ATTORNEYUnited States Patent Office 3,3 l2, l d6 Patented Apr. 4:, 19673,312,166 FLOW METER Merlin Davis, Washington, D.C., assignor to theUnited States of America as represented by the Secretary of the ArmyFiled Dec. 7, 1964, Ser. No. 416,658

9 Claims. (Cl. 73-194) Often it is desirable to be able to measure therate of flow of a fluid within a pipe, tube, conduit, or like vesselwhich, because of the size or location of the vessel carrying the saidfluid, it is impractical to measure by conventional means. It is one ofthe objects of this invention therefore to provide for suchmeasurements.

Furthermore, it has been found that in the measurement of the rate offlow of certain fluids that errors are caused by the insertion ofmeasuring devices into the fluid. For instance, in the measurement ofthe rate of flow of blood within blood vessels it has been found thatthe insertion of measuring devices into the blood causes theintroduction of errors due to the clotting of the blood around themeasuring devices. Therefore, it is a further object of this inventionto allow for the measurement of the rate of flow of fluids without thecausing of such clotting or crystalization of the measured fluid and theconcomitant errors in measurement which are introduced.

In order to achieve these objects, I rely upon a novel means ofmeasurement of fluid flow which employs the pumping of a fluid into theflow stream through two orifices such that the fluid injected into theflow stream is controlled to maintain the proportioning as the flow rateof the flow stream varies. One of the orifices faces up stream and theother faces downstream. The differential flow of the fluid from thesetwo orifices is a measure of the rate of flow of the fluid in the vesselto be measured if the solution is provided to the two orifices at acommon and substantially constant pressure. The measurement of thedifferential flow is achieved by employing a miniaturized rotameterwithin the tube leading to one of the above-mentioned orifices. Thefloat of this rotameter is made of magnetic material and forms the coreof a differential transformer The displacement of the float of therotameter, which is recorded electronically, provides a measure of therate of flow of the fluid within the vessel.

For a fuller understanding of the nature and objects of the invention aswell as for a specific embodiment thereof, reference should be had tothe following detailed de scription and the accompanying drawings inwhich:

FIG. 1 represents the embodiment of the invention as a device formeasuring the rate of flow of blood within a blood vessel;

FIG. 2 represents an enlargement of the rotameter;

FIG. 3 is an enlarged view of another modification of arotameter;

FIG. 4 is an elevational view, partly in section, of an injection probeincluding oppositely directed orifices; and

FIG. 5 is a view taken on the line 5-5 of FIG. 4.

Referring now to FIG. 1, the specific embodiment of the inventionemploys a constant displacement pump 1 which provides a substantiallyconstant flow of a saline solution 13 through two tubes 3 and i to twoorifices 5 and 6 placed within a tube '7 the flow of fluid within whichis desired to be determined. A valve 12 controls the flow of fluid intube 3. The plunger 2 of the pump 1 is actuated by a screw which in turnis operated by a wormgear reduction motor, not shown. Alignment is aidedby the use of a large ball between the end of the screw and the lunger2. Tube 7 represents a blood vessel and the fluid flow to be measured inthe embodiment is the rate of flow of the blood in the vessel. One ofthe tubes 4 leading from the constant displacement pump 1 is tapered tocontain a spherical float 8, made of a magnetic material, which acts asa rotameter The rotameter float 8 forms the core of a differentialtransformer 9 which is electronically connected to an oscillator andbucking amplifier 10 and a recorder 11 A float-core structure whichprovided an adequate linear range of operation consisted of a 0.7 mm.steel ball 14 cemented or held by magnetic attraction to a 0.6 mm.ferrite-Q ball 15 as shown in FIG. 3.

The operation of the device embodying the invention is as follows. Theessentially constant displacement plunger pump ll injects a solutionthrough two tubes 3 and 4 which are provided with longitudinally slottedorifices 5 and 6 positioned near their respective tips. The slot 5 ontube 3 is directed upstream against the flow of blood in the bloodvessel 7. The slots 6 on tube 4 is directed downstream with the flow offluid in the vessel 7. The combined saline discharge passing throughboth slots 5 and 6 will remain substantially constant provided the pump1 provides a relatively constant flow of saline to the two tubes 3 andlat a relatively high pressure compared with the forces developed by theblood pressure Within the blood vessel 7. The relative discharge throughthe slots 5 and 6 should remain constant in spite of pressure variationsin the vessel, resulting from static head fluctuations, since thesepressures are identical against both openings and therefore cancel outhydraulically.

Pressure variations due to changes in velocity head, on the other hand,are positive on one side and negative on the other, so that, althoughthe combined volume of saline pumped into the vessel from both tubes 3and t remains fixed, there will be a decrease of saline flow in one ofthe tubes and a compensating increase in the other tube.

To measure this differential flow rate a transducer is employed in theform of a rotameter which has been miniaturized for low flow rates. Thefloat 8 is made of a magnetic material and forms the core of adifferential transformer 9. Operation of the differential transformer 9is based on the essentially linear change of flux-linkage between aprimary coil and secondary coils, which are connected in seriesopposition, resulting from a vertical displacement of the core; in thiscase, the float 8. The float 3 is protected from straying by means of apermanent magnet (not shown). The induced signals are fed to anamplifier W, with provisions for bucking out the input no-flow signal,and subsequently passed on to a recorder 11.

Other constructions than that shown at 3 and 4 in FIG. 1 with slots 5and a may be used. In some controlled experimental research, Whereprecise volume flowrate measurements are required, a dual injectionneedle which is permanently mounted within a tube or cannula issatisfactory. In other work of a clinical nature, a probe may berequired in the form of a needle which can be used to puncture thevessel 7 for the purpose of recording average relative velocities. Aparticular design for this purpose is shown in FIGS. 4 and 5. A tube 16terminating in a point 22 to puncture vessel '7 and having an outsidediameter equal to that of a number 17 hypodermic needle and supported inan appropriate holder 17 is slotted as at 18; the slots being 0.006 to0.125 inch.

An eccentrically placed inner tube 19 is brazed to the outer tube 16,passes through holder 17 and is supported in a number 21 hypodermic head20. Tube 19 is also slotted as at 21 to the same dimensions as tube 16and the slot 21 is in register with one of the slots it; thus providingseparate oppositely disposed openings. Area 23 must be approximatelyequal to area 24.

I claim:

1. A device to measure the rate of flow of fluids comprising:

(a) fluid supply means for supplying fluid at a substantially constantrate of flow;

(b) bifurcated conduit means terminating in juxtaposed oppositelydirected outlets adapted to be injected into a fluid stream, the axis ofeach of said outlets being in a direction substantially parallel to theflow of the fluid stream, said fluid supply means connected to the inletof said bifurcated conduit means to supply fluid to the fluid streamthrough said conduit means;

() a rotarneter for measuring the rate of flow of the fluid stream,disposed in one branch of said bifurcated conduit means and includingmagnetic float means;

(d) differential transformer means disposed about one branch of saidbifurcated conduit means and positioned to include within the corethereof said magnetic float means; and

(e) amplifying and recording means connected to said differentialtransformer means for measuring the rate of flow of a fluid stream asdetermined by the displacement of said magnetic float means, saiddisplacement being proportional to the unbalance of the flow of thefluid supply in the bifurcated conduit means caused by the flow of thefluid stream.

2. A device as recited in claim 1 further including a valve in a branchof said bifurcated conduit means other than the branch including saidrota-meter.

3. A device to measure the rate of flow of a fluid stream in a conduitcomprising:

(a) fluid supply means for supplying fluid at a substantially constantrate of flow;

' (b) a bifurcated tubular member terminating in juxtaposed oppositelydirected outlets adapted to project into the fluid stream in the conduitthe axis of each of said outlets being in a direction substantiallyparallel to the flow of the fluid stream, said fluid supply meansconnected to the inlet of said bifurcated tubular member, to supplyfluid to the fluid stream in the conduit through said tubular member;

(c) a first branch of said bifurcated tubular member including a valveand a second branch having a por tion of restricted diameter;

(d) a rotameter for measuring the rate of flow of the fluid stream inthe conduit, disposed in said portion of restricted diameter in saidsecond branch of said bifurcated tubular member and including magneticfloat means;

(e) diffeerntial transformer means surrounding said restricted portionof said second branch of said bifurcated tubular member and positionedto include within the core thereof said magnetic float means; and

(f) recording and amplifying means connected to said differentialtransformer means for measuring the rate of flow of the fluid stream inthe conduit as determined by the displacement of said magnetic floatmeans, said displacement being proportional to the unbalance of the flowof the fluid supply in the branches of the bifurcated tubular membercaused by the flow of the fluid stream in the conduit.

4. A device as recited in claim 3 wherein said fluid supply meanscomprises a hypodermic syringe having a unidirectionally operatedplunger.

5. A device as recited in claim 3 wherein said magnetic float meanscomprises a steel ball.

6. A device as recited in claim 3 wherein said magnetic float meanscomprises a pair of connected balls of magnetic material and relativelydifferent diameters.

7. A device as recited in claim 3 wherein said bifurcated tube comprisesa pair of conduits joined at one end to a com .1011 inlet and extendingindependently from said common inlet in spaced relation and terminatingin juxtaposed position with the outlet of each conduit relativelydiametrically opposed.

8. A device to measure rate of flow of fluids compris- (a) fluid supplymeans for supplying fluid at a substantially constant rate of flow;

(b) bifurcated conduit means terminating in a probe adapted to beinjected into a fluid stream and having oppositely directed outletsadjacent the end thereof, so that when said end is injected into thefluid stream the axis of each of said outlets being in a directionsubstantially parallel to the flow of the stream, said fluid supplymeans connected to the inlet of said bifurcated conduit means to supplyfluid to the fluid stream through said conduit means;

(c) a rotarneter for measuring the rate of flow of the fluid stream,disposed in one branch of said bifurcated conduit means and includingmagnetic float means;

((1) differential transformer means surrounding one branch of saidbifurcated conduit means and positioned to include Within the corethereof said magnetic float means; and

(e) amplifying and recording means connected to said differentialtransformer means for measuring the rate of flow of a fluid asdetermined by the displacement of said magnetic float means, thedisplacement being proportional to the unbalance of the flow of thefluid supply in said bifurcated conduit means caused by the flow of thefluid stream.

Q A device as recited in claim 8 wherein said probe comprises:

(a) a first tubular member supported in a first holder and terminatingin a tip adapted to be injected into a fluid stream and diametricallyopposed outlets adjacent said tip;

(b) said holder having a bore communicating and aligned with the bore insaid tubular member;

(c) a second tubular member of lesser diameter than said first tubularmember and eccentrically secured internally of said first tubularmember, said second tubular member passing through an opening in saidfirst holder and supported in a second holder in juxtaposition to saidfirst holder; and

((1) said second tubular member having an outlet adjacent the free endthereof and in registry with an outlet of said first tubular member.

References Cited by the Examiner UNITED STATES PATENTS 2,009,427 7/ 1935Bentzel 73-202 FOREIGN PATENTS 545,848 7/1956 Italy.

RICHARD c. QUEISSER, Primary Examiner,

JAMES J. GILL, Examiner.

E, D. GILHOOLY, Assistant Examiner.

1. A DEVICE TO MEASURE THE RATE OF FLOW OF FLUIDS COMPRISING: (A) FLUIDSUPPLY MEANS FOR SUPPLYING FLUID AT A SUBSTANTIALLY CONSTANT RATE OFFLOW; (B) BIFURCATED CONDUIT MEANS TERMINATING IN JUXTAPOSED OPPOSITELYDIRECTED OUTLETS ADAPTED TO BE INJECTED INTO A FLUID STREAM, THE AXIS OFEACH OF SAID OUTLETS BEING IN A DIRECTION SUBSTANTIALLY PARALLEL TO THEFLOW OF THE FLUID STREAM, SAID FLUID SUPPLY MEANS CONNECTED TO THE INLETOF SAID BIFURCATED CONDUIT MEANS TO SUPPLY FLUID TO THE FLUID STREAMTHROUGH SAID CONDUIT MEANS; (C) A ROTAMETER FOR MEASURING THE RATE OFFLOW OF THE FLUID STREAM DISPOSED IN ONE BRANCE OF SAID BIFURCATEDCONDUIT MEANS AND INCLUDING MAGNETIC FLOAT MEANS; (D) DIFFERENTIALTRANSFORMER MEANS DISPOSED ABOUT ONE BRANCH OF SAID BIFURCATED CONDUITMEANS AND POSITIONED TO INCLUDE WITHIN THE CORE THEREOF SAID MAGNETICFLOAT MEANS; AND (E) AMPLIFYING AND RECORDING MEANS CONNECTED TO SAIDDIFFERENTIAL TRANSFORMER MEANS FOR MEASURING THE RATE OF FLOW OF A FLUIDSTREAM AS DETERMINED BY THE DISPLACEMENT OF SAID MAGNETIC FLOAT MEANS,SAID DISPLACEMENT BEING PROPORTIONAL TO THE UNBALANCE OF THE FLOW OF THEFLUID SUPPLY IN THE BIFURCATED CONDUIT MEANS CAUSED BY THE FLOW OF THEFLUID STREAM.